#!/usr/bin/env python3
"""
主程序入口文件
"""
def main():
 print("Hello, World!")
 print("Welcome to my project!")
if __name__ == "__main__":
 main()
def calculate_sum(a, b):
 return a + b

def calculate_diff(a, b):
 return a - b

def calculate_multiply(a, b):
 return a * b

def calculate_divide(a, b):
    if b != 0:
      return a / b
    return None